I'm not even going into the new 110x15 fork standard right now, we'll concentrate on 148x12.
142x12 came out about 3 years ago and quickly took the world by storm. Why? It promised a bit stiffer rear ends on FS bikes, compatibility via adapter for most existing hubs as the cassette and disc rotor stayed in exactly the same place, and something new to sell to the bike-buying public. Which I would roundly condemn, except that I'm one of the purveyors of said new stuff.
|27.5+? My doing.|
Enter "Boost" (why didn't 142x12 get a cool name?) 148x12 rear ends. The idea here is that you move both the cassette and disc rotor outboard 3mm, and move the flanges out to match. Result, you can move the *chainring* out a bit to make more room for the tire, keep a decent chainline, and end up with a bit stronger rear wheel to boot.
here's C'dale's explanation of the setup). Stupidmobile (you know, the 29er with 40cm chainstays?) was built this way. So are many bikes I build for customers, because it gives you a ton of benefits and really only has a few drawbacks. You can also do fun stuff like an 83mm low-q-factor fatbike by using various amounts of rear end offset (Felix's runs a 135x10 rear hub offset 10mm).
Whew. Did that all make sense? No? That's what I run into a lot. Many people don't like the idea of asymmetry, so the whole idea is off the table. I think that's a big part of the 148x12 idea - easier to explain, inherently less weird and threatening...but we don't do normal and unthreatening around here!
Ken wanted it *all*. 148x12, lots of tire clearance (in his case 27.5x2.8-3 or so) and short, short chainstays (well, not totally insane - we did 41.5cm). So we went nuts and did an *offset 148x12* setup. In this case, it's just 2mm of offset to get the chainline we wanted, but it still felt weird to take a brand new Anvil dummy axle and chuck it up on the lathe!
So long story short, Ken's bike is weird but should be awesome. Your bike can be awesome too if you think outside the box a bit and let me get creative - it's custom, folks. The world is your oyster.
Or we can just do 148x12, because what the heck, I already paid for the dummy axle, and the writing is on the wall...